A vehicle power supply device as follows has been conventionally proposed. A high-voltage battery is mounted in a vehicle and DC electrical power outputted from the battery is converted to AC electrical power by an inverter to supply electrical power to a plug socket (external output terminal) (see, for example, Japanese Patent Application Publication No. 2004-276672). Mounting the power supply device in the vehicle enables an operation of an electric device in the vehicle. Accordingly, for example, a mobile phone can be charged in the vehicle by connecting a charger of the mobile phone to the power supply device.
In such a power supply device, a power supply switch of the vehicle and an external output switch for turning on and off the output of electrical power stored in the battery are independently provided. Accordingly, even when the vehicle is stopped and the power supply switch is in an off state (OFF mode), the electrical power can be supplied from the battery as long as the external output switch is in an on state, and the power supply device has excellent usability.
However, when the external output switch is in the on state, the inverter for converting the DC electrical power to the AC electrical power is in an operational state. Accordingly, when this state continues for a long time, the electrical power stored in the battery is gradually consumed and eventually used up. Furthermore, the power supply device has a problem that, when a driver gets off the vehicle forgetting that the electric device is connected to the plug socket, the electrical power stored in the battery is unintentionally consumed and is eventually used up.
As described above, in the conventional vehicle power supply device, the power supply switch and the external output switch are independently provided. This causes a problem that, when a long time elapses with the external output switch being in the on state, the electrical power stored in the battery is unnecessarily consumed and eventually used up.